This invention relates to an internal combustion engine and more particularly to an improved decompression device for such engine.
As is well known, it is desirable to maintain a relatively high compression ratio for engines. By utilizing high compression ratios, greater specific output can be obtained. One disadvantage, however, with use of high compression ratios is that starting of the engine becomes more difficult. If electric starting is employed, the starter motor must be larger and more powerful as must be the drive between the starter motor and the engine. Where manual starting is utilized, the problems of high compression ratios are even greater.
There has been proposed, therefore, devices which operate so as to permit the engine to operate at a high compression ratio but which incorporate a device for reducing the compression ratio during starting. These decompression devices take many forms.
One way in which it is possible to reduce the compression ratio during starting is to open the exhaust valves for a brief period of time during the compression stroke. This will reduce the compression ratio and facilitate starting. The decompression device is then deactivated once the engine is started so that the maximum compression ratio can be enjoyed.
However, the provision of a mechanism for achieving this decompression is not as simple as it may appear. This is particularly true when the engine has multiple cylinders and multiple valves. It is basically desirable or even necessary to reduce the compression of all cylinders and this can be quite difficult and complex.
It is, therefore, a principal object of this invention to provide an improved and simplified arrangement for reducing the compression ratio than engine on starting.
It is a further object of this invention to provide an improved and simplified decompression device for engines having multiple valves and multiple cylinders.
This invention is adapted to be embodied in an internal combustion engine having a cam shaft with a plurality of cam lobes each of which cooperates with a follower for operating the valves of the engine. The cam shaft is formed with an axially extending bore in which an actuating cam member is supported for reciprocation. A plunger member is supported for reciprocation along an axis that is generally transversely disposed to this bore and which intersects at least one cam lobe in an area spaced from its tip portion. When the actuating cam member is moved in the bore, the plunger will be actuated and engage the follower and open the associated valve at a time during the stroke when the valve would normally be closed.